|Zero Point Module|
Height: 0.65 meters
- "It's kind of like a miniature universe in a bottle."
- —Rodney McKay
A Zero Point Module, often abbreviated ZPM and otherwise known as Potentia meaning power to the Quindosim, is an incredibly long-lived power source of great magnitude capable of powering entire cities and intergalactic spacecraft for thousands of years, making it the cleanest and most potent energy source in the known universe. Current physics suggests that no power source with greater unit yield is theoretically possible.
- "It extracts vacuum energy from [an] artificial region of subspace-time until it reaches maximum entropy."
- —Dr. Radek Zelenka
Created by the Ancients millions of years ago, ZPMs are capable of generating massive amounts of energy, which is drawn from a pocket of subspace-time known as the quantum foam (subatomic wormholes constantly opening and closing and fading in and out of subspace). As a ZPM supplies power to a system, the pocket slowly destabilizes itself until it collapes entirely, having been stripped of all its inherent energy; how quickly this process occurs appears to be directly proportionate to the amount of power being supplied. Once the pocket collapses the ZPM is no longer able to supply power and becomes, for all intents and purposes, useless. 
ZPMs have a potential life of many millions of years, and the amount of power generated by three of them is sufficient enough to power an energy shield over a city the size of Manhattan for 10,000 years whilst under the pressure of several thousand feet of water as well as orbital bombardment, and can easily allow for intergalactic hyperspace travel. Even just one ZPM can easily power a shield to survive the most powerful energy weapons in existence for several hours, lift a city-ship weighing millions of tons (plus any water caught in the shield bubble) off a planet, send it into hyperspace, then complete a successful landing on another world with more than enough energy left to supply much of the city-ship's primary and secondary systems for at least several more months, and fire multiple salvos consisting of thousands of drone weapons.  
Like many types of Ancient technology, Zero Point Modules are crystal-based. The crystals that compose the shell of the ZPM are similar in many ways to the crystals adapted by the Goa'uld and Tok'ra: red crystals contain the necessary programs to allow ZPMs to provide power to Ancient technology when a ZPM is interfaced with a conduit, while yellow crystals act as a buffer to prevent catastrophic overload. The crystals of a ZPM are virtually indestructible and can remain functional for hundreds of thousands of years. 
- "I didn't believe my eyes: three ZPMs right in front of me."
- —Elizabeth Weir
Although the Ancients and Asurans were able to produce ZPMs as needed, every ZPM discovered and used by the Tau'ri and Wraith have been obtained from either leftover Ancient technology and outposts or the Asuran homeworld. It is unlikely that any of the ZPMs found were ever full, as they were all supplying power to a previous system for an unknown period of time (the only possible exceptions being the module hidden on Dagan and the one in Ra's possession).
The first ZPM encountered by the Tau'ri was on the planet of Proclarush, which was later used to power drone weapons of the Ancient outpost in Antarctica to destroy the Goa'uld fleet under the control of Anubis. It was later depleted powering the Stargate in order to dial an intergalatic address, allowing the Atlantis Expedition to reach Atlantis in the Pegasus Galaxy. It was later given to Ba'al as a ruse. In an alternate reality the Tau'ri never learned the location of Atlantis, and the ZPM was instead drained fending off an Ori attack.  
Atlantis, and every other known city-ship, relied on ZPMs in groups of three to supply power, and so is typically unable to properly function with other means due to insufficient energy generation. After the Ancients returned to Earth, three ZPMs were left behind to work with city's shield and hold back the ocean. By the time the Atlantis Expedition arrived 10,000 years later, two of them were completely depleted and the third was drained soon after. 
Rodney McKay discovered a ZPM on M7G-677, where it was used to power a strong electromagnetic field around the planet's Stargate. The device the ZPM was tied to was used to disrupt Wraith technology, thus protecting the planet. McKay brought it to Atlantis in the hope of using it to power the city, but soon returned it after learning that it was much too depleted to be of any use to them. 
Camulus found an Ancient outpost with a ZPM nearly half full. Camulus couldn't figure out how to properly use the device (possibly because he lacked the ATA gene), so he rigged the ZPM to explode if it was ever linked to an electrical charge. Bill Lee estimated that if detonated, the tampered ZPM had the energy potential to completely destroy Earth, while Samantha Carter estimated that it likely would have destroyed the entire solar system. It's unknown what happened to this ZPM after they realized that it was tampered with, but it was likely sent to Area 51 for study. 
There was a ZPM on Dagan that was left behind by the Brotherhood of the fifteen when the planet was culled by the Wraith several centuries ago, who in turn received it from the Ancients for safekeeping. The Atlantis Expedition would have obtained it to defend against the Wraith fleet headed for Atlantis, however a number of the planet's inhabitants formed a new Brotherhood and took the ZPM when they realized that the people from Atlantis weren't the Ancients. 
SG-1 discovered a ZPM in Egypt that had previously belonged to the Goa'uld Supreme System Lord Ra. It was later used to once again power the Stargate and dial Atlantis, and then to allow the Daedalus to arrive in Atlantis in only four days. The ZPM was then used to power Atlantis' shield and protect it from a Wraith assault, and then to trick the Wraith into believing that Atlantis was destroyed by a nuclear warhead. After providing power to Atlantis for nearly two years, the ZPM was depleted to allow an alternate Rodney McKay to return to his own reality.  
The Genii once had access to a ZPM. Ladon Radim claimed that he stole it from the Brotherhood of the Fifteen, however Atlantis discovered that the ZPM had been long depleted and was stored in the Genii archives. Ladon used the depleted ZPM to further his coup d’état, and it was likely destroyed in the nuclear explosion he used to destroy the Genii leadership. 
When a group of Ancients were discovered traveling the void between the Pegasus and Milky Way galaxy at close to the speed of light, the Daedalus returned them to their city. Upon arriving in Atlantis the Ancients asked the Expedition to leave, and created three ZPMs to power their city. After the Asurans attacked and subsequently occupied Atlantis, Atlantis 1 was able to destroy the Asurans and acquire the ZPMs. Despite McKay's vehement protests, two were sent back to Earth (one to power the Antarctic outpost and another to power the Odyssey), while one remained on Atlantis. 
Later, the ZPM in Atlantis was nearly depleted by an attack by the Asurans using a special satellite. The Expedition used their sole ZPM, along with additional power from the drilling platform, to power the city's stardrive. However, due to damage inflicted to the power conduits by the satellite, Atlantis dropped out of hyperspace far too early, leaving the city-ship stranded in empty space. The damage had caused them to leak power, and by the time they repaired enough of the damage to safely complete the journey they didn't have enough power left to jump to back into hyperspace. Realizing that Asuras was within range of an experimental hyperdrive equipped to a puddle jumper, John Sheppard, Rodney McKay, Ronon Dex and Elizabeth Weir traveled to the planet to steal one of the Asuran's ZPMs.
Thanks to Weir's newly-activated nanites they managed to infiltrate the Asuran's subspace communication network and easily steal a ZPM. As McKay was interfacing the ZPM with the jumper's hyperdrive to return them to Atlantis, an Asuran ship revealed itself to prevent the jumper from leaving. Fortunately, the Apollo dropped out of hyperspace and distracted it long enough to allow the jumper to board Apollo, which immediately jumped to hyperspace. Upon their return to Atlantis the ZPM was quickly used to take Atlantis to M35-117, its new home. The ZPM then took on the role of powering Atlantis, with plenty of power left to suite their needs. 
When the Wraith fought alongside the Tau'ri and Travelers in the Battle of Asuras, they managed to steal several ZPMs from Asuras before the planet was destroyed. A number of them were used to power a Wraith cloning facility to bolster their numbers enough to defeat the Tau'ri in the same manner they defeated the Ancients. The ZPMs were most likely destroyed when the hive-ship Atlantis had commandeered was driven into the facility. Todd also used a number of other ZPMs he stole from Asuras to power a hive-ship, which had the effect of making it nearly invincible. Powered by ZPMs, the hive-ship was powerful enough to defeat three 304's upgraded with the latest Asgard technology and make the intergalactic hyperspace journey to Earth. 
Realizing that no other ship they had was powerful enough to destroy the upgraded hive-ship, the Atlantis Expedition gleaned the locations of two more of Todd's stolen ZPMs and used them to power Atlantis' stardrive, returning the city to its original home to defend it. After arriving in orbit around Earth Atlantis and its stockpile of drone weapons went blow-for-blow with the hive-ship, but not even the Ancient city was powerful enough to destroy the hive without severely compromising its own safety. After the hive-ship was destroyed by a nuke detonated inside of its structure, Atlantis was forced to make a landing on Earth, cloaked to ensure the continuing secrecy of the Stargate program. Atlantis successfully landed, albeit damaged.They currently reside in San Francisco. 
- Matter bridge
- Project Arcturus
- Zero-point energy
- ZPM-powered hive-ship
Behind the scenes
- Most of the characters, American and otherwise, in both shows pronounce the "Z" in "ZPM" as "Zee" whereas McKay, a Canadian, pronounces the "Z" as "Zed".
- Janus seemed to have forgotten what Elizabeth Weir called ZPMs and Niam was confused when Rodney was talking about ZPMs until he explained their operation, implying that the Ancients and Asurans had a different name for them.
- The MGM Tech Journal mentions that a singularity exists within the module, which somewhat contradicts on-show descriptions of the ZPM. It is possible, however, that the singularity is either a wormhole that leads to the pocket of subspace-time or the pocket itself rather than the heart of a black hole.
References and notes
- Stargate SG-1: The DVD Collection 52